The present invention relates to an apparatus, method and program for alarming abnormality in tire air-pressure.
As a method for alarming abnormality in tire air-pressure to detect decrease in tire air-pressure and issue an alarm, for example, a method for detecting whether or not a tire air-pressure is decreased due to a variation in a determinate value calculated from a rotational velocity of each tire by utilizing the fact that a rotational velocity of a tire having a decreased pressure is faster than that of a tire having a normal air-pressure, and issuing an alarm when decrease in tire air-pressure is detected, has been conventionally used (see Japanese Unexamined Patent Publication No. 305011/1988).
In the above-mentioned method, determinate values DEL (1) to (3) are calculated by the following equations, for example:DEL(1)={(V1+V4)/2−(V2+V3)/2}/{(V1+V2+V3+V4)/4}×100(%);DEL(2)={(V1+V2)/2−(V3+V4)/2}/{(V1+V2+V3+V4)/4}×100(%); andDEL(3)={(V1+V3)/2−(V2+V4)/2}/{(V1+V2+V3+V4)/4}×100(%),wherein V1 to V4 represent wheel velocities of a front left tire (FL tire), a front right tire (FR tire), a rear left tire (RL tire) and a rear right tire (RR tire), respectively in the above-mentioned equations. In a case where any one of the determinate values DEL (1) to (3) exceeds a predetermined threshold, decrease in tire air-pressure is notified to a driver.
However, in some cases where the rotational velocity of the tire changes by causes other than the decrease in the tire air-pressure, for example, in the case where a vehicle carries out long-distance traveling, so that a diameter of a tire is smaller, an alarm was issued even at a normal internal pressure.